In recent years, a non-destructive inspection technique using a high frequency electromagnetic wave (hereinafter refer to as “terahertz wave”) having an arbitrary band in the region from the millimeter wave to the terahertz wave (from 30 GHz to 30 THz) has been developed. It is known that there exist many absorption lines of various substances including biomolecules in the terahertz wave region. Therefore, as an application field of this frequency region, there is a technique for performing the imaging as a safe fluoroscopic inspection device, instead of the X-ray fluoroscopic inspection device. Further, the application field of this frequency region also includes a spectroscopic technique for examining the bonded state of molecules by obtaining an absorption spectrum and a complex dielectric constant in a substance. Further, an analysis technique of biomolecules, and a technique for evaluating the carrier concentration and mobility, or the like, are also expected as the application field of this frequency region.
As an inspection device in which a terahertz wave is used, a constitution as shown in FIG. 21 is disclosed (Japanese Patent Application Laid-Open No. 8-320254). As shown in FIG. 21, this inspection device is constituted to irradiate an object with a terahertz wave propagated through space, and to thereby measure constituent materials of the object on the basis of changes in the propagation state of the wave transmitted from the object.
However, in general, the terahertz wave is strongly absorbed by moisture. For this reason, when the terahertz wave is propagated in the atmosphere, as in the case of Japanese Patent Application Laid-Open No. 8-320254, the terahertz wave is greatly attenuated by the absorption due to moisture in the atmosphere. Thus, it is desired to detect a specimen by using a technique in which the electromagnetic wave is confined in a certain region so as to be transmitted, by the use of a waveguide technique, for example, an optical fiber waveguide, such as used in many electromagnetic wave techniques and optoelectronic techniques, in order to reduce the attenuation of the terahertz wave. It is shown that the terahertz wave is propagated through a single line path which is formed by a conductor so as to serve as a fiber-shaped waveguide for propagating the terahertz wave (“Nature”, vol. 432, p 376-379, 2004).
Further, for detecting a specimen by using the fiber waveguide without the use of the terahertz wave range, there is proposed an optical fiber type specimen inspection device for measuring a trace of specimen in high sensitivity (Japanese Patent Application Laid-Open No. 2001-174406). As shown in FIG. 19, this specimen inspection device is constituted such that optical fiber waveguides are arranged so as to face each other with a certain gap. On the end surface of this fiber waveguide, materials having different refractive indexes are periodically arranged so that a resonance structure is formed. Thereby, a specimen which exists in the gap can be measured in high sensitivity.
A case where the waveguide technique using the optical fiber as disclosed by Japanese Patent Application Laid-Open No. 2001-174406 is applied to the terahertz wave is considered. In this case, the optical fiber waveguide is formed only by dielectric materials. Thus, depending upon the materials to be used, the propagation characteristic of the terahertz wave is affected by the frequency dependence of physical properties of the materials. Specifically, when the terahertz wave has a certain frequency region, it is conceivable that the propagation loss and dispersion characteristic of the terahertz wave are changed in accordance with frequency, and hence, the propagation waveform of the terahertz wave is greatly changed during the process of propagation in the waveguide. For this reason, such optical fiber waveguide is undesirable as a waveguide for propagating the terahertz wave. As a result, there is a need for a waveguide having more excellent propagation characteristics.
Further, in the specimen inspection device disclosed by Japanese Patent Application Laid-Open No. 2001-174406, it is difficult to make the device constitution small, because the optical fiber waveguides need to be arranged so as to face with each other, and an external mechanism for such arrangement is needed.